Detroit Mayor Mike Duggan said a power outage put city schools , firehouses , police stations , City Hall and Wayne State University in the dark Tuesday morning .

Speaking at a press conference , Duggan said power had been restored to about one third of the customers by 2 p.m. ET and that power probably will be restored to all by the end of the day .

The outage affected about 900 locations , including 36 fire stations and 81 city schools , according to the Detroit website .

Public schools dismissed students after the power went out . Duggan said the dismissal went smoothly .

The mayor said there had been no spike in police or fire calls while power was out . About 18 state troopers helped 78 officers direct traffic at intersections while traffic signals were out of service , he said . Schools and other public buildings should be back in service Wednesday , officials said .

The city website said 740 traffic signals were knocked out , but power was not lost for the 911 system .

The outage occurred about 10:40 a.m. ET when a Public Lighting Department -LRB- PLD -RRB- power cable and then a circuit breaker failed , he said .

The City of Detroit is going through bankruptcy . As part of the process , the city is getting out of the business of running PLD and the utility corporation DTE Energy is taking over , Duggan said . DTE Energy assisted the city in bringing the system back online .

`` All we know at this point is that the cable went to ground , which means it grounded itself out , '' said Jerry Norcia , president and chief operating officer for DTE Electric and Gas Storage & Pipelines . `` So it could be a breach in the insulation or it could be many other circumstances that caused that cable to fail . ''

Detroit has experienced notable power outages in the past .

Just last Sunday , power went out during a professional hockey game at Joe Louis Arena . Detroit 's Comerica Park lost power last year during the American League Championship Series .

The outage trapped some people in elevators in several government buildings , and firefighters were trying to free them , fire Chief Dale Bradley said .

This outage is n't believed to have affected residences , officials said .

Duggan said he 'd earlier asked DTE to focus on those circuits that fail the most and review them .

The cable that failed Tuesday was not one that had done so previously , authorities said .

The power outage wo n't affect Tuesday night 's professional hockey game , said Todd Beam , Red Wings director of public relations .

`` We are back at full power at Joe Louis Arena , '' he said . `` The game will be played as scheduled at 7:30 p.m. tonight . ''

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Detroit mayor says he hopes power will be restored by end of day

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Power goes out at public buildings

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People trapped in elevators in several government buildings

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More than 80 Detroit public schools dismiss students early